In drilling wells for water, oil, etc., or in otherwise making an extended hole in the ground, for the same purpose, it is known that one winds up with a hole of a certain depth, at the bottom of which is the liquid that is to be drawn up from the ground, preferably by placing a pump or other device in the well.
It has become commonplace to provide a well screen at the bottom of the well, to screen out sand and other particulate material from the zone at the bottom of the well, so that a pump may be lowered into the well, to pump the liquid under conditions in which the pump will be free of particulate material that might otherwise be damaging. Even in those instances when a pump is not inserted into the bottom of the well, as for example when suction devices are used, it is still nevertheless desirable to have sand or other particulate material screened out of the liquid entering the hole. Accordingly, it has become commonplace to construct well screens and to place them at the bottom of the well. Frequently, such screens are generally cylindrical in shape, and usually have the lower end closed off, with an open upper end, for attachment of a pipe or similar conduit to the well screen at its upper end. Thereafter, a number of lengths of pipe may serially be connected together, as needed, to provide for delivery of liquid from the well screen, to a location generally above ground.
In recent years, well screens have been constructed of synthetic polymeric materials, such as polyvinyl chloride (PVC), because of the corrosion resistant characteristics of such materials, as well as their bacteria resistant characteristics.
Such well screens may be made in a single piece, or in multiple sections that are secured together, by heat sealing, solvent sealing, vibration sealing, or other forms of sealing or welding, as may be desired, some of which are discussed in U.S. Pat. No. 4,352,512, the entire disclosure of which is herein incorporated by reference. Also, fittings of various pipe sections together, and of the lower-most pipe section to a well screen, or of well screens one to the other, in serial fashion, may be made by any suitable technique, such as by the bayonet type locking arrangements integrally molded with the screens and pipe sections, such as is also disclosed in the above-mentioned patent, particularly when the screens are constructed of a molded polymeric material in which the protrusions and recesses of the bayonet type of locks may be readily integrally molded therewith.
Additionally, when the well screens are constructed of moldable material, it is known to mold rigidifying supports, of both the radial or ring-like type, and of the upstanding, inwardly directed and axially or longitudinally extending type, as part of the well screen, integral therewith, for efficiency and economy in construction. In addition to the disclosure of the above-mentioned patent, reference is made in this regard to U.S. Pat. No. 4,262,744, the complete disclosure of which is also herein incorporated by reference. In this patent also, it is taught that a plurality of spaced slots may be formed in the skin extending therethrough with the slots disclosed in portions of the skin located between adjacent compression ribs, and with the slots extending essentially entirely around the periphery of a preferably tubular well screen, in order to maximize filtration over the surface of the well screen.